Nearly ferromagnetic spin-triplet superconductivity

Spin-triplet superconductors potentially host topological excitations that are of interest for quantum information processing. We report the discovery of spin-triplet superconductivity in UTe2, featuring a transition temperature of 1.6 kelvin and a very large and anisotropic upper critical field exceeding 40 teslas. This superconducting phase stability suggests that UTe2 is related to ferromagnetic superconductors such as UGe2, URhGe, and UCoGe. However, the lack of magnetic order and the observation of quantum critical scaling place UTe2 at the paramagnetic end of this ferromagnetic superconductor series. A large intrinsic zero-temperature reservoir of ungapped fermions indicates a highly unconventional type of superconducting pairing.

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Tuning magnetic confinement of spin-triplet superconductivity

npj Quantum Materials ◽

10.1038/s41535-020-00270-w ◽

2020 ◽

Vol 5 (1) ◽

Author(s):

Wen-Chen Lin ◽

Daniel J. Campbell ◽

Sheng Ran ◽

I-Lin Liu ◽

Hyunsoo Kim ◽

...

Keyword(s):

Applied Pressure ◽

Upper Critical Field ◽

Magnetic Confinement ◽

Superconducting Phase ◽

Zero Field ◽

First Order ◽

Diode Oscillator ◽

Spin Triplet ◽

First Order Transition ◽

Tunnel Diode Oscillator

Abstract Electrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41 T applied along the crystallographic b axis (hard axis) of UTe2 as a function of temperature and applied pressures up to 18.8 kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16 kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity.

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Absence of Superconductivity in the Hubbard Dimer Model for κ-(BEDT-TTF)2X

Crystals ◽

10.3390/cryst11060580 ◽

2021 ◽

Vol 11 (6) ◽

pp. 580

Author(s):

Dipayan Roy ◽

R. Torsten Clay ◽

Sumit Mazumdar

Keyword(s):

Low Temperatures ◽

Magnetic Order ◽

Organic Superconductors ◽

Density Matrix Renormalization Group ◽

Magnetic Fluctuations ◽

Zero Temperature ◽

Dimer Model ◽

Density Matrix Renormalization ◽

Superconducting Pairing ◽

Direct Calculations

In the most studied family of organic superconductors κ-(BEDT-TTF)2X, the BEDT-TTF molecules that make up the conducting planes are coupled as dimers. For some anions X, an antiferromagnetic insulator is found at low temperatures adjacent to superconductivity. With an average of one hole carrier per dimer, the BEDT-TTF band is effectively 12-filled. Numerous theories have suggested that fluctuations of the magnetic order can drive superconducting pairing in these models, even as direct calculations of superconducting pairing in monomer 12-filled band models find no superconductivity. Here, we present accurate zero-temperature Density Matrix Renormalization Group (DMRG) calculations of a dimerized lattice with one hole per dimer. While we do find an antiferromagnetic state in our results, we find no evidence for superconducting pairing. This further demonstrates that magnetic fluctuations in the effective 12-filled band approach do not drive superconductivity in these and related materials.

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